In a wearable device including an acceleration sensor, for example, a timestamp is given to the value of the acceleration measured in the case of detecting the motion of a person. Furthermore, by a data collecting device, measurement messages given the timestamp are collected and the behavior of the person is estimated in some cases.
For example, in the case in which one person wears plural wearable devices and observation of coordination of arms and legs is attempted, it is difficult to correctly estimate the behavior if the timestamps given by the respective wearable devices do not match the same time clock basis.
In the case of attempting to make the timestamp given by the wearable device match the basis of a system time clock in the data collecting device, besides an error in a local clock of the wearable device, an error generated in the data collecting device also becomes an obstacle.
Examples of the related art are disclosed in Japanese Laid-open Patent Publications No. 2010-164346, No. 2007-027985, and No. 2007-258800.